Positron emission tomography (PET) is rapidly becoming essential in diagnosis of heart and neurological conditions and is also useful in the staging and assessment of cancer treatments. PET is also a valuable research tool for studying in vivo biochemical functions during either normal or disease states. A drawback to PET is the necessity of a large capital investment. Still, the growth of PET as a procedure and the acquisition of PET scanners by medical centers is expected to grow rapidly over the next few years and the development of mobile PET units may be near.
Every PET scanner or instrument must be calibrated using radioisotope sources containing a positron emitter. Additionally, virtually every clinical scan must be accompanied by a patient "transmission scan" to permit proper image interpretation. All of the commercial calibration and transmission sources for current clinical PET scanners use germanium-68.
Germanium-68 has a half-life of about 271 days, decays by electron capture to gallium-68, and lacks any significant photon emissions. Gallium-68 decays by positron emission. These properties make germanium-68 an ideal isotope for calibration and transmission sources. Additionally, gallium-labelled imaging agents such as disclosed in U.S. Pat. No. 5,079,346 can employ gallium-68 produced from a germanium-68/gallium-68 generator. Thus, the availability of the long-lived parent, germanium-68, is of significant interest because of its generation of the shorter-lived gallium metal activity. The useful shelf-life is determined by the activity of the germanium-68, while the short half-life of the gallium-68, about 68 minutes, minimizes the radiation dose to technicians during calibration of PET scanners and the patient transmission scans.
Previously, germanium-68 has been recovered from an irradiated rubidium target. In such a recovery process, the rubidium target is generally dissolved in 4 Normal (N) to 9 N HCl, followed by distillation of the germanium and other volatiles such as arsenic and selenium. The germanium is then selectively recovered from the distillate by extraction with carbon tetrachloride. A second extraction of the carbon tetrachloride solution with water yields an aqueous solution of the germanium. While this process proves suitable for recovery of the germanium from the rubidium targets, other sources of germanium are not as easily processed by this procedure.
Irradiated molybdenum targets have generally served as a source for the separation of strontium, yttrium, zirconium and rubidium isotopes. Such irradiated molybdenum targets have now been found to contain a significant amount of germanium-68 that has previously gone unrecovered. Such irradiated targets also contain quantities of niobium and arsenic that may also be sought to be recovered. Recovery of these isotopes would provide additional supplies for the medical community. Optionally, recovery of germanium via an organic solvent-free process may be desirable to minimize waste.
Accordingly, it is an object of this invention to provide a process for the recovery of germanium-68 from irradiated molybdenum targets.
Another object of this invention is to provide a process for selectively separating both the niobium and the germanium from irradiated molybdenum targets.
Yet another object of this invention is to provide a process for selectively separating both the germanium and the arsenic from irradiated molybdenum targets.
Still another object of this invention is to provide a process for selectively separating the niobium, arsenic and germanium from irradiated molybdenum targets.
It is a further object of this invention to provide an organic solvent-free process for recovery of germanium-68.